Design for Durability and Strength Through the Use of Fly Ash and Slag in Concrete


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Title: Design for Durability and Strength Through the Use of Fly Ash and Slag in Concrete

Author(s): R. N. Swamy

Publication: Special Publication

Volume: 171


Appears on pages(s): 1-72

Keywords: Blast furnace slag; chlorides; concretes; durability; fly ash; high-performance concrete; high-strength concrete; microstructure; mix proportioning; porosity; pore-size distribution.

Date: 8/1/1997

This paper presents a critical evaluation of the use of fly ash and ground granulated blast-furnace slag in concrete. In order to develop a rational concrete mixture incorporating these siliceous materials, their inherent characteristics are assessed, including their limitations and weaknesses. Based on the mixture proportioning methodology advocated, it is shown that fly ash and slag concretes, having the same three-day cube strength as concrete without them, can be produced. Engineering implications of using these materials such as increased bleeding and times of setting, reduced heat of hydration, low-early strength, and slow rate of gain of strength are addressed, and the need and role of a minimum period of moist curing to mobilize the chemically-bound qualities of these materials are fully emphasized. It is shown that both high-early strength and high-strength concrete can be achieved with fly ash and slag. Even with all their limitations, the durability properties of concretes with fly ash and slag are superior to those of concrete made with portland cement alone. It is shown further that extremely fine siliceous materials are only of limited use in concrete, but that a moderate increase in fineness, about thrice that of portland cement, can not only preserve and fully use the benefits of fineness on a variety of engineering properties such as bleeding, time of setting and heat evolution, but also lead to excellent chemical resistance and durability with high strength at early and later ages. It is shown that a slag fineness of about 1200 m2/kg can produce concretes of high strength and exceptional durability.